Research On Low-Frequency Wideband Lightweight Multilayer Composite Absorbing Materials

With the continuous development of radar detection technology,the demand for lowfrequency broadband absorption materials is increasing.Traditional absorption materials mainly work in the frequency range of 2-18 GHz.When the working frequency range is extended to lower frequencies,the thickness of the material will significantly increase,which is difficult to meet the requirements of engineering applications.In response to these issues,this thesis proposes a universal method for constructing a low-frequency ultra-wideband composite absorption structure based on a multi-layer periodic structure and efficient absorption honeycomb,and carries out experimental verification.The specific research work is as follows:1.In engineering applications,periodic patterns must be printed or etched on the medium substrate.However,the traditional equivalent circuit model did not consider the influence of the substrate,resulting in insufficient calculation accuracy.To address this issue,this thesis analyzes the electromagnetic coupling effect between the substrate and the periodic structure,and corrects the equivalent inductance and capacitance to obtain an accurate surface impedance analytical formula for the periodic pattern loaded on the medium substrate,laying the foundation for constructing an accurate model of multi-layer periodic structure equivalent circuit.2.In response to the problem of insufficient accuracy of traditional absorptive honeycomb equivalent electromagnetic parameters,this thesis first starts from the doublelayer structure of the absorptive honeycomb impregnated with soaking slurry,and obtains the high-precision equivalent electromagnetic parameters of the absorptive honeycomb through a two-step equivalent method.Compared with the two reported equivalent methods for absorptive honeycomb electromagnetic parameters,the method proposed in this thesis has higher accuracy and better universality.Based on this method,the reflectivity of multi-layer gradient absorptive honeycomb was further calculated,and the results of theoretical analysis and simulation calculation were consistent,verifying the reliability of the equivalent method proposed in this thesis.3.Based on the above work,an accurate equivalent circuit model of a composite absorber structure consisting of multi-layer periodic structures and absorbing honeycomb was constructed,providing a theoretical method for the efficient optimization design of wideband composite absorber structures.Under the guidance of this method,a wideband composite absorber structure with a thickness of 35 mm and a working frequency band of0.82～18 GHz was designed and experimentally verified,with a relative bandwidth of182%.According to Roznaov’s theory,the theoretical limit thickness corresponding to the reflection spectrum of this structure is 33.5mm,and the structure designed in this thesis only exceeds the theoretical limit thickness by 4%.Further analysis of the electric field distribution and energy loss of the structure reveals the working mechanism of the wideband absorber.The calculation results of the equivalent circuit model,numerical simulation results,and experimental test results are in good agreement,verifying the effectiveness of the design method proposed in this thesis.